l6i 



species studied, Xenopsylla cheopis are considered the 

 most efficient transmitting agents "because they are more 

 readily infected when fed on septicemic "blood, and they 

 transmitted the disease to many more guinea pigs. They 

 also tend to "become "blocked earlier and to remian in- 

 fectious for a longer time than other fleas. Blocked 

 cheopis are very persistent in their efforts to o"btain 

 blood ..." 



According to Lien-teh, Chun, Pollitzer, and Wu (1936), 

 Xenopsylla astia is not as important as X. cheopis in the 

 transmission of plague though it may "be the responsible 

 vector in certain circumscribed and isolated outbreaks. 

 X. "brasiliensis is the predominant rat-flea of Uganda, 

 Kenya and Nigeria, and has "been known to transmit plague 

 from rat to rat and from rat to man. Nosopsyllus fasciatus , 

 the so-called European rat-flea, attacks man less readily 

 than X. cheopis and does not predominate on rats in plague 

 areas. Leptopsylla musculi likewise does not readily "bite 

 man and is of minor importance in the spread of the 

 disease. 



In some parts of the world plague is harbored in ani- 

 mals other than the rat. In such cases the ectoparasites 

 of these animals are of importance in maintaining the 

 disease. Chief of these are Diamanus montanus , found on 

 the ground squirrels of California; Oropsylla silantiewi ; 

 found on the tarbagan of Mongolia; . Ceratophyllus tes quorum , 

 carried by the suslik or marmot of Southeastern Russia; 

 and Dinopsyllus lypusus found on the gerhille of Africa. 



As indicated in the list of arthropods above, "besides 

 fleas, other insects including flies, ants, "beetles, mos- 

 quitoes, and roaches have also "been suspected of carrying 

 plague "bacilli. 



Data concerning the possible role of ticks in the trans- 

 mission of plague is very meager. Skorodumoff, in 1928, 

 (quoted "by Lien-teh, et al. , 1936) was among the first to 

 o"btain positive experimental results. He infected a wild 

 mouse and a guinea pig from crushed suspension of ixodid 

 ticks. In 1929, Tikhomirova and Nikanoroff (Lien-teh, et 

 al. , 1936) found three ticks ( Ixodes autumnal is ) upon the 

 carcass of an experimentally infected tara"bagan. The 

 tissues of these ticks yielded positive cultures of the 

 plague "bacillus and was infective to guinea pigs. Faddeeva 

 (1932) fed Ar gas persicus on infected guinea pigs when the 

 "bacteremia was most marked. Both the inoculation and the 

 culture experiments gave positive results. Borzenkov and 

 *Donskov (1933) reported the finding of plague bacilli in 

 Ixodes autumnal is and Rhipicephalus schulzei taken from 

 animals infected with plague (see also Gaisky (I93I)). 

 These workers also found that HyalomTna volgense , from 



